This invention relates to packaging and interconnecting means for microcircuit chips which are contained in chip carriers of the general class and type now being adopted in the electronics industry.
Until fairly recent times, solid state microelectronic devices were produced with twelve or fourteen active areas and these devices were packaged in prismatic rectangular insulating bodies, dual in-line packages in DIPs, having leads from the active areas extending from two opposite sides of the rectangular bodies. More recently, microcircuit devices had been produced in the form of square chips having active areas along all four side edges thereof and these new generation chips are somewhat smaller than the previous microcircuit devices, notwithstanding the fact that the more recent chips require more leads from their active areas.
A standard packaging arrangement is being used for the newest family of microcircuit devices and is sponsored by the Electronics Industry Association and the National Electric Manufacturers Association. This standard chip carrier, and a socket which is adapted to receive the standard chip carrier, is described in Aviation Week and Space Technology, Jan. 24, 1977. In general, a standard chip carrier in accordance with the specifications of the associations noted above comprises a square low-profile container having at least six leads extending from all four laterally facing side surfaces thereof. It is common practice to mount chip carriers of this type directly on the printed circuit boards or to removably insert such chip carriers into chip carrier sockets, which are dimensioned to receive a single chip carrier.
It should be mentioned that in the rapidly developing microelectronics industry, added requirements are continually emerging for microcircuit chips so that a packaging arrangement which may be entirely satisfactory for the microcircuits being produced today may be totally incapable of accommodating, and providing the necessary interconnections for, the microcircuit chips which will be available only a few years hence. For example, chips such as microprocessor chips are presently being manufactured which have an information capacity of 4000 information bits (4K). Within the next few years, chips having the same dimensions as presently available chips will have a capacity of 8K and it is also foreseen that 16K bits will be available shortly thereafter. It follows that manufacturers who adopt a packaging arrangement capable of accommodating only the presently available 4K chips will be faced with a problem in the near future of changing over to a system having the capability of handling 8K bits and thereafter they will be required to again change to a system having capabilities sufficient for the 16K bits.
In accordance with one aspect of the instant invention, we provide a chip carrier socket which is capable of receiving in stacked relationship, one on top of the other, a plurality of standard chip carriers and connecting the leads of these chip carriers to the conductors on a printed circuit board or to other external conductors. When presently available chips are connected to a printed circuit board in accordance with this aspect of the invention, the present chips can be replaced by future generation chips having added information storage capacity without other significant changes to the overall packaging arrangement; thus, two 4K bits might be replaced by one 8K bit at some future time when the 8K bits become available. This changeover could be accomplished by retrofitting or alternatively as a running change in a manufacturing process. In accordance with another aspect of the invention, we provide a chip carrier socket which also functions as an interconnecting means for connecting preselected and predetermined leads of several chip carriers in a stack to each other and to the conductors of a printed circuit board. In accordance with this aspect of the invention, bus bars in the socket are selectively interrupted to achieve the desired circuit paths. In each case, the area required on the printed circuit board is substantially reduced by virtue of the stacked arrangement of the chip carriers in the socket. Other advantages which are described below are also achieved.
It is accordingly an object of the invention to provide an improved chip carrier socket. A further object is to provide a chip carrier socket capable of receiving a plurality of chip carriers. A further object is to provide an interconnecting and packaging means for a plurality of microcircuit chips. A further object is to provide an interconnecting and packaging means for a plurality of identical microcircuit chips which may, at some future time, be replaceable by a lesser number of chips, the packaging means being capable of accommodating the future generation microcircuit chips with a minimum of rearrangements of other portions of the product being manufactured.